1. Field of the Invention
The present invention relates to centripetal air bleed means in a compressor rotor of a turbomachine such as an airplane turboprop or turbojet.
2. Description of the Related Art
The bladed wheels of a compressor rotor are connected together by a tubular wall forming a substantially cylindrical or frustoconical surface of revolution that extends coaxially between the disks. This wall connecting the disks together may be formed integrally with a first disk or it may be put into place and fastened, e.g. by brazing or welding, at one of its axial ends on a lateral face of the first disk, and its opposite axial end may include an annular flange fastened, e.g. by nut-and-bolt type means, to a second disk.
It is known to fit the rotor with centripetal-flow air bleed means for feeding systems for ventilating and/or cooling downstream stages of the compressor and turbine rims of the turbomachine, and also for purging the turbomachine.
In the prior art, these bleed means comprise passages formed through the wall connecting together the compressor disks and opening out into an annular chamber formed inside the wall between two rotor disks.
A portion of the air flowing in the flow section of the compressor is bled off via the through passages in the wall of the rotor, and it passes into the annular chamber where it flows centripetally along the disks of the rotor, and then flows from upstream to downstream inside the turbomachine and outside an axial cylindrical sheath, in order to reach the turbine. However, turbulence and head losses in the annular chamber between the rotor disks are considerable, which leads to air being bled from a downstream stage of the compressor and therefore leads to an increase in the specific consumption of the turbomachine.
Furthermore, the bleed air is heated because of its high speed of rotation compared with that of the disks. When the air entrainment coefficient Ke (which is equal to the ratio of the tangential speed of the bleed air flowing in the turbomachine divided by the speed of rotation of the rotor of the turbomachine compressor) is greater than 1, it is necessary to increase the flow rate of the bleed air in order to ensure proper cooling of the components of the turbine. However, in certain zones, in particular in the interdisk chamber and in the vicinity of the cylindrical sheath, the coefficient Ke may be as high as 2.5 in the prior art.
In order to reduce that drawback, proposals have been made to mount an annular row of radial tubes in the chamber between the disks, which tubes are fastened to the disks around the sheath by appropriate means (see document EP-A1-1 262 630). The air bled through the through passages in the connection wall is constrained to pass along the radial tubes, which turn at the same speed as the disks. The air leaving these tubes comes to the level of the cylindrical sheath at a speed that is equivalent to that of the disks (Ke=1), thereby making it possible to limit head losses and to limit the increase in the temperature of the bleed air.
Nevertheless, the head losses at the inlet to the annular chamber remain high. Furthermore, the means for fastening the radial tubes are complex since they need to limit vibration of the tubes when in operation, thereby leading to relatively high costs and to an increase in weight.